The invention relates to a compressed-air actuated disk brake according to the preamble of claim 1 which is provided particularly for road vehicles and preferably for commercial vehicles.
Compressed-air actuated or pneumatic disk brakes of the above-mentioned type are known, for example, from German Patent Document DE-OS 37 16 202 as well as German Patent Document DE-OS 40 32 885. In the case of these known disk brakes, a caliper, which is disposed to be displaceable in the axial direction, reaches around a brake disk, in which case a compressed-air actuated brake application device is arranged on one side of the caliper. When the brake application device is actuated, a brake shoe situated on this side of the brake disk presses against the latter, whereupon, because of the reaction forces, the caliper is displaced in the opposite direction and, as a result, presses a brake shoe situated on the opposite side also against the brake disk.
In the case of these known disk brakes, the brake application device comprises a pivoting lever as the actuating element which, by means of an essentially semicircular pivot bearing, is disposed so that it can be swivelled about an axis of rotation which extends in parallel to the plane of the brake disk. The pivoting lever comprises an actuating arm whose end region engages with the pressure piston of a brake cylinder in such a manner that, when compressed air is admitted, a corresponding swivelling of the pivoting lever will take place. On its side facing the brake disk, the pivoting lever rests, by means of an eccentric, approximately in the longitudinal center, against a traverse structure. The traverse extends in parallel to the axis of rotation and is guided to be slidable with respect to the brake disk. At least one adjusting spindle having an external thread is adjustably screwed into a respective assigned internal thread of the traverse. Each adjusting spindle acts, by way of a pressure member disposed on its brake-disk-side end, upon the brake shoe which is disposed in the caliper on the brake application side so that it can be displaced with respect to the brake disk. The brake shoe consists of a brake lining and a metallic pressure plate which is acted upon by the pressure member of the respective adjusting spindle.
In the case of these known disk brakes, it is a basic problem that the weight must be kept as low as possible in order to minimize the unsprung masses of the vehicle. However, particularly the construction of the application device and of the caliper must be as stable and as torsionally rigid as possible in order to ensure good efficiency and a low hysteresis of the brake. It is therefore very difficult to significantly reduce the weight of the brake while maintaining the necessary qualitative characteristics. Thus, it was found, for example, that even the torsional strength of the pivoting lever becomes increasingly important because any torsion will considerably impair the running properties of the lever bearings which has a direct effect on the efficiency and the hysteresis. Pivoting levers used so far, for optimizing the efficiency and the hysteresis, have therefore been constructed to be largely massive and in one piece in order to achieve a torsional strength which is as high as possible.
It is an object of the invention to develop a compressed-air actuated disk brake according in such a manner that, while a high efficiency and a low hysteresis is maintained, a certain weight reduction can be achieved.
According to the invention, this object is achieved by the use a fork-shaped pivoting lever.
Surprisingly, tests have shown that a useful alternative to a massive pivoting lever is the use of a fork-shaped pivoting lever in which two legs extend or fork from the end region of its actuating arm a semicircular pivot bearing and the bearing of the eccentric are in each case formed by corresponding pairs of bearings in the end regions of the legs. Such a fork-shaped lever has a significantly lower weight than a massive pivoting lever so that the overall weight of the disk brake and the unsprung masses are correspondingly reduced. Furthermore, comparatively high savings of material are achieved.
However, in further tests, it was found that, in the case of such fork-shaped pivoting levers, torsional strains may nevertheless occur, specifically in the two legs. As a result, it cannot always be avoided that the (total of four) bearings of the pivoting lever and of the eccentric actuated by it have optimal running properties so that, under certain circumstances, a certain impairment of the hysteresis behavior and of the coefficient of friction will occur.
According to another aspect of the invention according to the teaching of claim 2, which is considered important, this problem is solved by the fact that the arrangement of the two bearings in each leg as well as the course of the two legs is selected such that the theoretical points of the introduction of force of these two bearings (viewed from above) are situated essentially on the center line of the respective leg, as illustrated in the top view in FIG. 3. By means of this measure, it is achieved that the introduction of force does not deviate from the center line of the leg, which has the result that virtually no torsional strains are built up in the fork-shaped pivoting lever. Therefore, no transverse stress is applied to the bearings so that these bearings operate with the optimal coefficient of friction and almost free of any hysteresis.
According to the further development of the invention, the supporting of the eccentric in the pivoting lever may take place by means of a pair of bearings arranged between the eccentric and the traverse and/or by means of a pair of bearings arranged between the eccentric and the pivoting lever, slide bearings being preferably used for these bearings. In contrast, in the case of the two semicircular pivot bearings by means of which the pivoting lever is supported in the brake housing, roller bearings are preferred. However, under certain circumstances, slide bearings may also be used here. In addition, with respect to the optimal bearings, reference is made to German Patent Application DE-OS 42 12 384, which is no prior publication. Reference is made here to the full content of the disclosure of that patent document.
In the following, the invention will be explained in detail by means of embodiments with reference to the drawing.